WebApi v2 ExceptionHandler not called

Question

How comes that a custom ExceptionHandler is never called and instead a standard response (not the one I want) is returned?

Registered like this

Answer 1

The real culprit here is CorsMessageHandler inserted by EnableCors method in message processing pipline. The catch block intercept any exception and convert into a response before it can reach the HTTPServer try-catch block and ExceptionHandler logic can be invoked

protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
    CorsRequestContext corsRequestContext = request.GetCorsRequestContext();
    HttpResponseMessage result;
    if (corsRequestContext != null)
    {
    try
    {
        if (corsRequestContext.IsPreflight)
        {
        result = await this.HandleCorsPreflightRequestAsync(request, corsRequestContext, cancellationToken);
        return result;
        }
        result = await this.HandleCorsRequestAsync(request, corsRequestContext, cancellationToken);
        return result;
    }
    catch (Exception exception)
    {
        result = CorsMessageHandler.HandleException(request, exception);
        return result;
    }
    }
    result = await this.<>n__FabricatedMethod3(request, cancellationToken);
    return result;
}

Answer 2

Turns out the default only handles outermost exceptions, not exceptions in repository classes. So below has to be overridden as well:

public virtual bool ShouldHandle(ExceptionHandlerContext context)
{
    return context.ExceptionContext.IsOutermostCatchBlock;
}

UPDATE 1

WebAPI v2 does not use IsOutermostCatchBlock anymore. Anyway nothing changes in my implementation, since the new code in ShouldHandle still prevents my Error Handler. So I'm using this and my Error Handler gets called once. I catch errors in Controllers and Repositories this way.

public virtual bool ShouldHandle(ExceptionHandlerContext context)
{
    return true;
}

UPDATE 2

Since this question got so much attention, please be aware that the current solution is the one linked by @JustAMartin in the comments below.